Roll changing arrangement for a rolling mill

ABSTRACT

The disclosure of this invention relates to a rolling mill wherein the chocks of the work roll on the drive side of the mill are split to enable the work rolls to be removed and replaced while strip is still being passed between the rolls. The chocks of the work rolls on the operating side are nested. The work roll chocks are provided with wheels which, during the roll changing operation, are carried by a pair of upper tracks secured to the housings and chocks of the upper backup roll and by a pair of lower tracks carried only by the housings. A lower track runs past the front of the mill to a side shifting unit having tracks which serve as continuations of the lower tracks and which receive the wheels of the chocks of the operating side work roll and the wheels of the chock of the lower drive side work roll as the rolls are brought to and from the mill to transfer them from and to the side shifter. The wheels of the chock of the upper drive side work roll are held apart after the drive side chocks leave the mill by a plunger displaced by a cam and cam track. In an attempt to improve the productivity of rolling mills, and particularly high-speed tandem cold mills, much effort in recent years has been given to developing a system that would allow the work rolls of one or more stands to be changed while a strip is still passing through these stands and is being rolled by the other stands of the mill.

United States Patent [1 1 Shumaker [451 July 24, 1973 ROLL CHANGINGARRANGEMENT FOR A ROLLING MILL Charles Storer Shumaker, Glenshaw, Pa.

[73] Assignee: Wean United, Inc., Pittsburgh, Pa.

[22] Filed: Mar. 27, 1972 [21] Appl. No.: 238,308

[75] Inventor:

Primary Examiner-Milton S. Mehr AttorneyHenry C. Westin [57] ABSTRACTThe disclosure of this invention relates to a rolling mill wherein thechocks of the work roll on the drive side of the mill are split toenable the work rolls to be removed and replaced while strip is stillbeing passed between the rolls. The chocks of the work rolls on theoperating side are nested. The work roll chocks are provided with wheelswhich, during the roll changing operation, are carried by a pair ofupper tracks secured to the housings and chocks of the upper backup rolland by a pair of lower tracks carried only by the housings. A lowertrack runs past the front of the mill to a side shifting unit havingtracks which serve as continuations of the lower tracks and whichreceive the wheels of the chocks of the operating side work roll and thewheels of the chock of the lower drive side work roll as the rolls arebrought to and from the mill to transfer them from and to the sideshifter. The wheels of the chock of the upper drive side work roll areheld apart after the drive side chocks leave the mill by a plungerdisplaced by a cam and cam track.

In an attempt to improve the productivity of rolling mills, andparticularly high-speed tandem cold mills, much effort in recent yearshas been given to developing a system that would allow the work rolls ofone or more stands to be changed while a strip is still passing throughthese stands and is being rolled by the other stands of the mill.

10 Claims, 5 Drawing Figures I PAIENIEB HLMH saw 1 0F 4 PAIENIEU JUL 2 4I973 SHEET b 0F 4 fllllllw nurfllll ROLL CHANGING ARRANGEMENT FOR AROLLING MILL The present invention provides an improved mill arrangementfor economically and efficiently carrying out the aforesaid object.

It provides a work roll chock and supporting arrangement that allows thework rolls to be held and transferred into and out of the mill withoutinterfering with the passing strip.

More particularly, the present invention provides for the drive sidechocks of the work rolls to be split and the upper chock to be carriedby a first track and the lower chock by a second track, whereas theoperating side chocks of the work roll are nested in which the low chockthereof is received in the upper chock, and the operating side lowerchock is carried by the second track, whereas the operating side upperchock is carried by both the first and second tracks and in which theupper drive side chock, when this chock passes beyond the tracks, issupported by the lower drive side chock.

It is a further feature of the present invention to provide for thelower tracks to extend beyond the front of the mill to a side shifterhaving tracks serving as extensions of the lower tracks of the mill andwhich tracks support the chocks of the operating side and the lowerdrive side chock when the rolls are being changed, displaceable means onsaid lower drive side chock for engaging and supporting the upper driveside chock when it is not being supported by said upper track.

These objects, as well as other novel features and advantages of thepresent invention, will be more fully appreciated when the followingdescription is read along with the accompanying drawings, of which:

FIG. 1 is an elevational view of one of the stands of a tandem millincorporating the features of the present invention, I

FIG. 2 is an elevational view at the operator's side of the window ofthe mill shown in FIG. I,

FIG. 3 is a sectional view taken on line 3-3 of FIG. I illustrating'thedrive side windows of the mill shown in FIG. 1,

FIG. 4 is a sectional view taken on line 4-4 of FIG. 2, and

FIG. 5 is a sectional view taken on line 5-5 of FIG. 2.

In referring first to FIG. 1, there is Illustrated a rolling millcomprising two upright spaced-apart housings l0 and 11, each of which,according to customary designs, is provided with windows 12 and 13 intowhich are received the bearing chock assemblies of the rolls of themill. The rolls comprise work rolls 14 and 15, each of which is backedup by backup rolls l6 and 17, respectively. The work roll 14 has bearingchock assemblies 18 and 19, whereas the lower work roll has bearingchock assemblies 22 and 23. Likewise, the backup rolls have bearingchock assemblies 24.

The chocks of the lower backup roll 17 are carried in a roll changingsled 25, the lower surface of which is received in the windows 12 and13. The chocks 24 of the upper backup roll 16 are adapted to be engagedby screws, not shown, arranged in each housing 10 and 11, FIG. 1actually showing the chocks 24 of the upper backup roll 16 separatedfrom the screws since this drawing is meant to depict the roll changingposition of the work rolls. The sled 25 at the bottom of the mill restson pistons of piston cylinder assemblies 28 arranged in the lowerportion of each housing 10 and II. The work rolls 14 and 15 are adaptedto be driven and for which purpose there are provided driving spindles31 connected to a power source, not shown.

At the operator's side of the mill there is provided a platform 33 and aside shifter 34, the functions and descriptions of which will be givenlater.

Reference will now be made to FIGS. 2 and 3 in order to more fullydescribe the characteristics of the chocks of the rolls 14, 15, 16 and17. FIG. 2 depicts the characteristics of the front or operating sidechocks of the work rolls l4 and 15 and associated mill elements. In thisconnection, it will be noted that the chock 18 of the upper work roll 14has downwardly extending leg portions 36 that provide an opening 37 forreceiving the vertical sides of the lower front work roll chock 22. Theadjacent vertical surfaces of these chocks are provided in the usualmanner with liners 38. Similar liners are provided between the housing10 and the outside vertical surfaces of the chock of the upper work roll14, in which connection it will be noted that the housing is indented byportions 42. Wheels 40 are provided at the lower portions of the chock22, and, while not seen in FIG. 2, they do appear in FIGS. 1, 4 and 5.The work roll chocks I8 and 22 are equipped with balance cylinderassemblies 43 arranged in the lower chock 22, which are retracted inview of the fact that the drawing depicts the roll changing position ofthe components.

In still referring to FIG. 2 and with reference to the chock 24 of theupper backup roll 16, it also is provided with downwardly projectingportions 43a which terminate into tracks 44. These tracks have guidingsurfaces adapted to guide and support wheels 45 provided at the top ofthe front chock 18 of the upper work roll 14. Somewhat larger wheels 46are provided in the legs 36 of the chock 18 which engage tracks 47mounted in the housings l0 and 11. These tracks, as illustrated in FIGS.1, 4 and 5, run from the front of the mill through the space between thehousings and terminate at the back of the housing 11, actually having anextended portion 48 beyond the housing 11, the purpose of which will bedescribed later. The vertical surface of operating side chocks 24 of thebackup rolls l6 and 17 are provided with the usual liners 49 that allowthem to slide vertically relative to the housing 10.

Referring now to FIG. 3, which depicts the back or drive side of therolling mill, it will be noted that the chocks l9 and 23 of the workrolls l4 and 15 are split in counter-distinction to the nestedrelationship of the work roll chocks I8 and 22 at the operating side ofthe mill. This split construction allows the chocks l9 and 23 to beaxially moved in and out of the. mill without interfering with a strippassing between the rolls I4 and 15. The chock 19 of the upper roll 14has lined vertical surfaces that engage projecting portions 51 of thehousing 11, which portions are protected by liners 52. At the top of thechocks 19, horizontal extending wheels 53 are provided which engagetracks 54 extending downwardly from the chock 24 of the backup roll 16.The tracks 54, as shown in FIG. 3, are actually hinged to the drive sidechock 24 by pins 55 and serve as extensions for both the tracks 44, aswell as tracks 56 formed on the chock 24 similar to the tracks 44 of thefront backup chock 24. It will be noted, and which is confirmed bylooking at FIG. 1, that the hinge construction just described is alsoemployed with respect the chock 23 is provided with balance cylinderassemblies 59, shown retracted in view of the roll changing position ofthe mill components. The drive side backup chocks 24 for the backuprolls l6 and 17 are provided with vertical liners 60-that allow forvertical movement of the backup chocks.

More specifically referring now to the various tracks earlier identifiedand the wheels of the chocks that engage them, reference will be made toFIGS. 1, 4 and 5, in which regard it will be noted that the two pairs ofwheels 40 and 46 of the front work roll chocks l8 and 22 generally fallin thesame longitudinal plane. As one views FIG. 4, the foremost wheels40 mounted on the work roll chock 22 of the lower roll fall immediatelyahead of the wheels 46, which are secured to the leg portions 36 of thechock 18 of the upper work roll 14. Since the upper work roll 14 mustmove towards the lower roll 15 to set the pass opening of the millduring rolling, the tracks 47 are provided with slots 63 immediatelybelow the operating position of the wheels 46 of the upper work rollchock 18. In order to support the upper chock until the wheels 46 passover theslots 63, a pair of wheels 45 at' the top of the chock 18 arespaced to the left of the wheels 46, as one views FIG. 4, and duringroll changing are in engagement with the tracks 44. During the periodwhile roll changing that the wheels 46 are in the slot areas, the chock18 is only supported by the wheels 45, whereas, during the remainder ofthe time, the chock will be supported by both the wheels 45 and thewheels 46.

Referring now to the drive side chock 23 of the lower work roll 15, thetwo pairs of wheels 58 are spaced apart with reference to the length ofthe slots 63 in the rails 47 so that, in removing the rolls from themill, the chock 23 will be supported by the back wheels 58 while thefront wheels 58 are passing over the slot 63. The reverse will takeplace when the rolls are moved into the mill. In referring now to thechock 19 at the drive side of the work roll 14, its pair of wheels 53,as noted in FIG. 4, is arranged at the veryback of the chock assemblyso. that the chock l9can be supported by the track network 44, 54 and 56during the entire period that the work rolls are moved from the mill. Inorder to allow for the convenient transfer of the wheels 53 of the chock19 from the tracks 44 to the platform 33, and vice versa, the frontchock 24 of the backup roll 16 is provided with an extending portion 65on which the tracks 44 are formed and which cooperation with theplatform is shown in phantom at the left-hand side of FIG. 4.

It will be noted that the tracks 44, 54 and 56 only support the driveside upper chock 19 when the roll assemblies are in the mill during rollchanging. The chocks l9 and 23 are maintained apart when they are out ofthe mill at the same spaced distance they assume when in the mill byplungers 68 mounted at the back of the chock 23 for vertical movement ondisplacement of rollers 69.- As shown in FIG. 5, the plungers androllers are arranged inward of the tracks 47 so that the rollers do notcontact the tracks on axial movement of the rolls l4 and 15. The rollersare designed to contact cam tracks arranged in the vicinity of theplatform 33 just ahead of the outermost portion of the extension 65 ofthe front backup chock 24. The chock 19 has recesses 71 to receive andbe supported by the adjacent ends of the plungers 68 when the rollers 69are caused to rise on contact with the cam tracks 70.

In referring now to FIG. 1 and with reference to the platfrom unit 33,it will be notd that it is provided with a pair of tracks 72 which formcontinuations of the tracks 47 that service the lower work roll chocks22 and 23. The platform extends between the mill and the side shifter 34which is provided with two pairs of sideby-side tracks 73 for supportinga new pair of work roll assemblies to be inserted into the mill and apair of used work roll assemblies that are retracted from the mill. Thetracks of each of these pairs, depending on which pair is positioned infront of the mill, will serve as extensions of the tracks 72 of theplatform 33. The positioning of the tracks is brought about by a rack 74and pinion 75 which, through a motor 75a, drives the side shifter 34over tracks 76 in a direction parallel to the steel line of the mill.The side shifter itself is carried by a carriage 77 supported by wheelsand tracks 78 and driven to and from the mill by a motor 79. Thecarriage 77 also carries the platform 33 in which, when the carriage ispositioned in front of the mill, the far end of the platform rests on apad 80 carried by the housing 10.

There remains one additional element to be described that has referenceto the replacement of the work rolls l4 and 15, which is shown only inFIG. 1. As noted, the lower drive side work roll chock 23 is providedwith a hook 81 that is adapted to be engaged by a cooperative hookelement 82 connected to a ram 83. The ram is adapted to be driventhrough the mill by a power means, not shown. The front end of the ram83 is supported by two pairs of wheels 84 arranged to engage theextension 48 of the tracks 47.

A brief description of the withdrawal of the work roll assemblies willnow be given. As noted before, the drawings depict the roll changingposition of the various mill components, in which connection the lowerbackup roll 17 has been lowered on operation of the piston cylinderassemblies 28 to allow the lower work roll 15 to be lowered and itswheels 40 and 58 to engage the tracks 47. In a like manner, the upperbackup roll 16 has been raised to cause the tracks 44 and 56 to engagethe wheels 45 and 53, respectively.

The lowering and raising of the backup rolls l7 and 16, respectively,provide an opening between the work rolls and brings them out ofengagement with the strip passing through the mill. The raising of thechocks 24 of the backup roll 16 is accomplished by lifting themillscrews and operating the roll balance for the backup roll 16. Theactual amount or distance that the upper backup roll 16 is raised iscontrolled by the consideration that the wheels 46 of the front upperwork roll chock 18 must be brought into alignment with the tracks 47 andthe stroke of the plungers 68. The registry of the tracks can beaccomplished in any number of ways, for example, by a pin operated by apiston cylinder assembly that will position the upper chocks 24 relativeto the housings l0 and 11. As noted previously, the balance cylinders,for example, the work roll balance cylinders 43 and 59, are retracted soas to avoid their interfering with or contacting the strip as the rollsare moved axially.

Prior to the separation of the work rolls preparatory to roll changing,the carriage 77, which, as noted before, includes the platform 33, isbrought to a position in front of the mill and arranged so that an emptypair of tracks 73 is provided in front of the mill to receive the rollassemblies 14 and 15 to be removed from the mill. The rolls are removedby simply operating the ram 83 to cause the pair of rolls 14 and 15 withtheir chock assemblies to move over their associated tracks onto theplatform 33 and eventually onto the side shifter 34.-

As previously described, the relationship of the several wheels to thetracks and slots 63 provide that the rolls throughout the entiretransport will be supported in a manner that they are held out ofcontact with the strip passing between them. ParticularlY with respectto the chocks l9 and 23 at the drive side of the work rolls 14 and 15,they are individually supported in a spacedapart relationship and theirsplit construction allows them to be passed over and under the strippassing through the mill. In bringing the new roll assemblies into themill, the procedure is essentially reversed as above described, in whichthe side shifter 34 will position the new set of rolls in front of themill to be engaged by the ram 83, the drive side chocks being held apartby plungers similar to the plungers 68 until they pass the cam tracks70.

In accordance with the provisions of the patent statutes, I haveexplained the principle and operation of my invention and haveillustrated and described what I consider to represent the bestembodiment thereof.

I claim:

1. In a rolling mill comprising:

a housing,

a pair of working rolls arranged on the opposite sides of the passlineof said mill and each having a drive side bearing chock and an operatingside bearing chock received in said housing, 7

said bearing chocks at the respective ends of said working rolls beingarranged to form cooperative pairs of bearing chocks,

said cooperative pairs of bearing chocks at the drive side being splitin a manner that the adjacent surfaces thereof can be spaced from saidmill passline during roll changing,

said cooperative pair of bearing chocks at the operating side beingnested in a manner that one of the bearing chocks thereof is receivedand carried by the other bearing chock, and

means for supporting said drive side bearing chocks to maintain themspaced from saidmill passline when moved through said mill during rollchanging,

other means including a member movable in the direction of one of saiddrive side bearing chocks contained by said other drive side bearingchock for continuing said spaced supporting thereof when said drivesidebearing chocks are out of said mill during roll changing.

2. A rolling mill comprising:

a housing,

a pair of working rolls arranged on the opposite sides of the passlineof said mill and each having a drive side bearing chock and an operatingside bearing chock received in the housing,

the bearing chocks at the respective ends of the working rolls beingarranged to form cooperative pairs of bearing chocks,

means for supporting the drive side bearing chocks so as to maintainthem spaced from said mill passline when moved through said mill duringroll changing, and

other means including a member movable in the direction of one of saiddrive side bearing chocks contained by the other drive side bearingchock for continuing the spaced supporting thereof when the drive sidebearing chocks are out of the mill during roll changing.

3. In a rolling mill according to claim 2 wherein said movable member iscarried by one of said drive side bearing chocks movable towards andaway from said other drive side bearing chocks and arranged to engagesaid other drive side bearing chock, and

means arranged to engage said member when said pair of drive sidebearing chocks are out of said mill during roll changing.

4. In a rolling mill according to claim 3 wherein said member comprisesa plunger arranged in the lower of said pair of drive side bearingchocks displaceable vertically towards and away from the upper of saidpair of drive side bparing chocks and adapted to engage said upper driveside bearing chock when displaced upwardly, and

means arranged on one side and outside said mill for engaging saidplunger when said drive side bearing chocks are outside said mill duringroll changing.

5. In a rolling mill according to claim 4 wherein said means forengaging said plunger comprises a track, and

a roller carried by said plunger arranged to engage said track.

6. In a rolling mill according to claim 5 wherein the end of said trackadjacent said mill is sloped away from said plunger and said plunger isofa length sufficient to engage the slope portion of said track, andwherein said slope is sufficient to cause said plunger to rise adistance sufficient to continue said spaced supporting of said driveside bearing chocks.

7. A rolling mill according to claim 3 in which the first means includesa first pair of tracks arranged to suport the bearing chocks of theupper working roll and, in addition, includes a second pair of tracksarranged to support the drive side bearing chock of the upper roll,

said second pair of tracks having sloped portions,

said member comprising a pair of plungers to engage a different one ofthe sloped portions, 7

a third pair of tracks arranged tosupport the bearing chocks of thelower roll,

separate means carried by the upper-and lower drive side bearing chocksfor engaging in a supporting relationship said first and third pairs oftracks, respectively, for supporting the drive side bearing chocks inthe spaced-apart condition when passing through said mill during rollchanging,

said third pair of tracks being arranged to overlap the slope portionsin a manner that said uppermost drive side bearing chock is supportableby one or the other of the first and second pairs of tracks by means ofsaid plungers and separate means.

8. In a rolling mill according to claim 7 wherein said slope portionsand said plungers are transversely spaced from said third pair oftracks.

7 8 9. A rolling mill according to claim 2 in which the mill forsupporting the first track means, first means include a first pair oftracks having supportthe first track means being of a length sufficientto ing surfaces, a second pair of tracks having supporting maintain thedrive side bearing chocks spaced from surfaces arranged on the sameelevation as the supportthe mill passline while the chocks are moved ingsurfaces of the first pair of tracks and including through the mill,sloped portions which are arranged to overlap portions second trackmeans arranged to overlap a portion of of said first pair of tracks, andto assume a supporting the first track means and to be engaged by saidrelationship with said other means when the uppermost other means in amanner to continue said spaced drive side bearing chock is not beingsupported by the support for the uppermost drive side bearing chockfirst means, 10 when passing to and from the mill during roll 10. Arolling mill according to claim 2 in which the changing.

first means include first track means, and means in the UNITED STATESPATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 71.17 387 DatedJuly 2L1. 1973 lnvntofls) Charles Storer Shumaker It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

On the cover sheet insert item[30]--Foreign Application Priority DataApril 15, 1971 Great Britian Column L line 11' "notd" should read notedColumn 5, line l8, 'ParticularlY" should read Particularly Column 6,line 26, claim L1, "bparin'g" should read bearing Signed and sealed this19th day of March 197L (SEAL) Attest:

EDWARD M.FLETCIER,JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents USCOMM-DC 50376'P69 U.S. GOVERNHENT PRINTING OFFICE: I989OSi6-38l.

FORM PC1-1050 (10-69)

1. In a rolling mill comprising: a housing, a pair of working rollsarranged on the opposite sides of the passline of said mill and eachhaving a drive side bearing chock and an operating side bearing chockreceived in said housing, said bearing chocks at the respective ends ofsaid working rolls being arranged to form cooperative pairs of bearingchocks, said cooperative pairs of bearing chocks at the drive side beingsplit in a manner that the adjacent surfaces thereof can be spaced fromsaid mill passline during roll changing, said cooperative pair ofbearing chocks at the operating side being nested in a manner that oneof the bearing chocks thereof is received and carried by the otherbearing chock, and means for supporting said drive side bearing chocksto maintain them spaced from said mill passline when moved through saidmill during roll changing, other means including a member movable in thedirection of one of said drive side bearing chocks contained by saidother drive side bearing chock for continuing said spaced supportingthereof when said drive side bearing chocks are out of said mill duringroll changing.
 2. A rolling mill comprising: a housing, a pair ofworking rolls arranged on the opposite sides of the passline of saidmill and each having a drive side bearing chock and an operating sidebearing chock received in the housing, the bearing chocks at therespective ends of the working rolls being arranged to form cooperativepairs of bearing chocks, means for supporting the drive side bearingchocks so as to maintain them spaced from said mill passline when movedthrough said mill during roll changing, and other means including amember movable in the direction of one of said drive side bearing chockscontained by the other drive side bearing chock for continuing thespaced supporting thereof when the drive side bearing chocks are out ofthe mill during roll changing.
 3. In a rolling mill according to claim 2wherein said movable member is carried by one of said drive side bearingchocks movable towards and away from said other drive side bearingchocks and arranged to engage said other drive side bearing chock, andmeans arranged to engage said member when said pair of drive sidebearing chocks are out of said mill during roll changing.
 4. In arolling mill according to claim 3 wherein said member comprises aplunger arranged in the lower of said pair of driVe side bearing chocksdisplaceable vertically towards and away from the upper of said pair ofdrive side bparing chocks and adapted to engage said upper drive sidebearing chock when displaced upwardly, and means arranged on one sideand outside said mill for engaging said plunger when said drive sidebearing chocks are outside said mill during roll changing.
 5. In arolling mill according to claim 4 wherein said means for engaging saidplunger comprises a track, and a roller carried by said plunger arrangedto engage said track.
 6. In a rolling mill according to claim 5 whereinthe end of said track adjacent said mill is sloped away from saidplunger and said plunger is of a length sufficient to engage the slopeportion of said track, and wherein said slope is sufficient to causesaid plunger to rise a distance sufficient to continue said spacedsupporting of said drive side bearing chocks.
 7. A rolling millaccording to claim 3 in which the first means includes a first pair oftracks arranged to suport the bearing chocks of the upper working rolland, in addition, includes a second pair of tracks arranged to supportthe drive side bearing chock of the upper roll, said second pair oftracks having sloped portions, said member comprising a pair of plungersto engage a different one of the sloped portions, a third pair of tracksarranged to support the bearing chocks of the lower roll, separate meanscarried by the upper and lower drive side bearing chocks for engaging ina supporting relationship said first and third pairs of tracks,respectively, for supporting the drive side bearing chocks in thespaced-apart condition when passing through said mill during rollchanging, said third pair of tracks being arranged to overlap the slopeportions in a manner that said uppermost drive side bearing chock issupportable by one or the other of the first and second pairs of tracksby means of said plungers and separate means.
 8. In a rolling millaccording to claim 7 wherein said slope portions and said plungers aretransversely spaced from said third pair of tracks.
 9. A rolling millaccording to claim 2 in which the first means include a first pair oftracks having supporting surfaces, a second pair of tracks havingsupporting surfaces arranged on the same elevation as the supportingsurfaces of the first pair of tracks and including sloped portions whichare arranged to overlap portions of said first pair of tracks, and toassume a supporting relationship with said other means when theuppermost drive side bearing chock is not being supported by the firstmeans.
 10. A rolling mill according to claim 2 in which the first meansinclude first track means, and means in the mill for supporting thefirst track means, the first track means being of a length sufficient tomaintain the drive side bearing chocks spaced from the mill passlinewhile the chocks are moved through the mill, second track means arrangedto overlap a portion of the first track means and to be engaged by saidother means in a manner to continue said spaced support for theuppermost drive side bearing chock when passing to and from the millduring roll changing.